A liquid injection apparatus can supply a small amount of liquid droplets to a necessary place by a necessary amount. For example, such liquid injection apparatus may be an inkjet printer, a dispensing device, a 3D printer, or the like. The inkjet printer attaches the ink droplets to a desired position on a medium such as a paper to form an image and a letter. The inkjet printer includes an inkjet head which ejects the ink droplet according to print data. The dispensing device supplies reagent to a predetermined container by a predetermined amount in a drug discovery and a biotechnology field. The 3D printer realizes stereoscopic printing by supplying liquid resin to a predetermined place by a predetermined amount at a predetermined time. Each of the inkjet printer, the dispensing device, and the 3D printer has the liquid injection apparatus which injects a small amount of the liquid droplets according to the control data. The inkjet head is also one of the liquid injection apparatus.
A conventional inkjet head may comprise a structure having a base plate on which an ink pressure chamber is formed, a vibration plate laminated on the base plate, and a piezoelectric element formed on the vibration plate. A piezoelectric body of a thin film tends to deteriorate as a high voltage is continuously applied for a long time. The deterioration of the piezoelectric body shortens the lifetime of the inkjet head.